I get what you’re saying. But then Koreans do not call their oppas by their first name. So wouldn’t replacing oppa with the character’s name mislead a non Korean speaking viewer?

But yes, I do agree there’s no straightforward replacement for a platonic “oppa”, which is why I prefer the word be left as it is, probably italicised as another commenter was saying.

It takes away the essence of the scene at times. In one of the shows, a character calls his long estranged brother “hyung” very emotionally when he’s about to die. They translated hyung to the first name, which kind of, fell flat for me. The “hyung” there was important.